The invention relates to a method of forming an image by imagewise crosslinking a polymeric substance by ink jet printing a crosslinker onto it.
It has been known to form images by selectively crosslinking materials by applying light to a crosslinkable resin. The technique has been used for forming photoresists where, after uncrosslinked material has been removed, etching of metal or glass is carried out. The technique has also been used to form silk-screen or screen-printing materials where the uncrosslinked material is washed out of the screen to create the finished printing screen. Such techniques are disclosed in xe2x80x9cLight Sensitive Systemsxe2x80x9d by J. Kosar, published by John Wiley and Sons, Inc., New York, 1965, and in xe2x80x9cScreen Process Printingxe2x80x9d by J. Stephens, published by Blueprint (an imprint of Chapman and Hall), London, 1996.
These techniques, while successful, are expensive as they require expensive light imaging apparatus. Further they require expensive resins that will crosslink when exposed to light. There is difficulty in forming thick coats of crosslinked polymer as the light can not penetrate through thick crosslinkable resins, particularly when they are colored. Further, only very expensive imaging equipment could accurately produce fine quality images.
U.S. Ser. No. 09/089,903, filed Jun. 3, 1998, now abandoned, by Simons et al and entitled Method of Forming an Image describes a method of forming an image which comprises providing a coating of a crosslinkable polymeric substance on a substrate, applying a pattern of crosslinker to the coated substrate by ink jet printing to crosslink the polymeric substance in the pattern of the crosslinker, and washing the coated substrate to remove crosslinkable polymer in the area not having the pattern of crosslinker applied thereto. The substrate may be a screen printing screen.
There is a need for alternative methods of providing hardened polymeric images in layers of crosslinkable materials that are accurate and low in cost.
A particular problem with the method of the noted U.S. Ser. No. 09/089,903 is that transporting some substrates, for example, a screen mesh through an ink jet printer is difficult.
The invention provides a method of forming an image comprising:
providing a coating of a crosslinkable polymeric substance on a first substrate,
applying a pattern of a first crosslinker to the coated first substrate by ink jet printing to crosslink the polymeric substance,
washing the coated first substrate to remove the crosslinkable polymer in the areas not having the first crosslinker applied thereto, and
transferring the crosslinked polymer on the first substrate to a second substrate.
Another embodiment of this invention provides a method of forming an image comprising:
providing a coating of a crosslinkable polymeric substance on a first substrate,
applying a pattern of a first crosslinker to the first coated substrate by ink jet printing to crosslink the polymeric substance in the applied pattern of the crosslinker,
washing the coated first substrate to remove the crosslinkable polymer in the areas not having the pattern of the first crosslinker applied thereto,
patternwise transferring crosslinked polymeric substance to a foraminous substrate,
bringing the foraminous substrate into contact with a receiving material,
applying an ink to the foraminous substrate, and
removing the foraminous substrate to leave a pattern on the receiving material.
This invention can provide accurate low cost silk screens and colored relief images on a variety of substrates using materials that are not light sensitive.
The invention has numerous advantages over previous processes of forming crosslinked images in crosslinkable materials. The invention is low in cost and can use a common ink jet printer to create accurate and low cost images. This printing technique allows images to be formed by printing from a computer onto a substrate that does not have to be kept in the dark. The substrate may be formed of a dry material that may be easily handled in the light and then washed with water to remove uncrosslinked polymer. The material does not need to be flat during imaging as in many light exposing techniques.
The method is much simpler to operate than existing decoration or fabrication techniques using light-induced hardening of polymeric layers by light exposure through an optical pattern. It does not involve light-sensitive materials, nor toxic materials like potassium dichromate. It provides a versatile decoration and fabrication technique to anyone with a computer and ink-jet printer fitted with a suitable cartridge, and has the potential to open a wide range of craft applications involving decoration and images to a large number of people. These and other objects will become apparent from the detailed description below.
The invention comprises a process for printing, marking or fabricating images, patterns or marks from electronic information by writing by means of ink-jet printing means which deposits in a pattern a first crosslinker onto a first substrate which bears a layer of crosslinkable or hardenable polymeric material, and then treating the first substrate to cause a distribution of hardened or crosslinked polymeric material according to the deposited pattern. The crosslinked polymeric material pattern is then transferred to a second substrate, for example, a screen printing screen.
The pattern of crosslinked polymeric material may constitute the desired image, or may be subsequently treated, for example, by dyeing to give the desired image. The image may then be used as a mask for a subsequent process, such as printing or etching.
The first substrate may be regarded as a temporary support as the pattern of hardened or crosslinked polymer is transferred from the first substrate to the desired second substrate.
Transfer may be achieved by contacting the second substrate with the pattern of crosslinked polymer on the first substrate, arranging for the crosslinked polymer to adhere preferentially to the second substrate, and then separating the first and second substrates.
A number of ways of arranging for the crosslinked polymer to adhere preferentially to the second substrate are available. For example, it may be possible to choose appropriate materials such that the second substrate has a natural affinity for the crosslinked polymer that is greater than the crosslinked polymer affinity for the first substrate.
Alternatively, transfer may be achieved by contacting the second substrate with the pattern of crosslinked polymer in the presence of an agent which promotes adhesion of the crosslinked polymer to the second substrate. For example, the adhesion promoting agent may comprise a layer of polymeric material attached to the second substrate which has a higher affinity for the crosslinked polymer. Alternatively, the second substrate may bear a second crosslinker agent (either a second quantity of the first crosslinker or a different type of crosslinker) that causes the crosslinked polymeric material in contact with the second substrate to crosslink further and thereby become attached preferentially to the second substrate. The second quantity or type of crosslinker may be applied to the first substrate after washing instead of or in addition to its application to the second substrate. Additionally, the second substrate may be pre-treated with polymeric or other materials that increase the effect of the adhesion promoting agent.
The first substrate may be any suitable material for printing with an ink jet printer. Suitable materials include cloth, metal, paper and plastic sheets. If a plastic sheet is used for the substrate it may be any of the common polymer sheet materials such as polyethylene, polypropylene, cellulose acetate and polyester.
The second substrate may comprise a foraminous material such as a permeable woven or fibrous material, such as silk fabric, polyester or polyamide mesh, or open-weave paper. In a particularly preferred embodiment of the invention, the second substrate is screen printing screen i.e. a screen mesh material suitable for use in screen printing. In this case, a pattern-wise distribution of crosslinked polymer will block the interstices of the mesh, for example, the spaces between the fibers, to allow silk-screen printing through the material onto another substrate.
The use of a fabric or mesh of cloth or metal is preferred as this allows the formation in a low cost manner of a screen-printing screen of high quality.
Any suitable crosslinkable polymeric material may be used in the invention. Typical materials include polymeric materials having carboxylic acid, amino, hydroxyl, unsaturated or epoxy functional groups. Suitable crosslinkable polymeric materials are gelatin, polymers of acrylic, methacrylic or maleic acid or anhydride or their copolymers with ethylene, styrene or vinyl ethers, and polyamine polymers such as polyethyleneimine. Most preferred is gelatin as it is safe, easily coated, and readily washed off if not crosslinked. The gelatin may be present with other polymeric materials, particularly carboxylic acid-containing polymers and gelatin-compatible latexes.
For example, gelatin has been found to be a suitable crosslinkable polymeric material, and suitable crosslinkers for gelatin are described below. After application of the pattern of crosslinking fluid, the unhardened gelatin may be removed by washing with warm ( greater than 35xc2x0 C.) water to leave a residual pattern of hardened gelatin, which may contain a dye or pigment, or may be subsequently dyed or pigmented.
Any suitable ink jet printer may be used in practice of the invention. The printer must be able to operate with a solution of the crosslinker substituted for the standard ink in the ink cartridge. As is known ink jet printers of the xe2x80x9cdrop on demandxe2x80x9d type generally operate by ejecting ink droplets by means of a pressure pulse induced by a piezoelectric impulse or by a thermal pulse (xe2x80x9cbubble jetxe2x80x9d). Either type of printer is suitable for the invention, provided that the solution of the crosslinker is formulated to have chemical and physical properties, including viscosity and surface tension, appropriate to the printer.
Other types of ink jet printer may also be used, including xe2x80x9ccontinuous workingxe2x80x9d types which eject a continuous stream of droplets which are deflected by an electrostatic field as required, while other types may use a long array of ink jet nozzles. The transport of the substrate to be printed can be varied to suit. For instance, film or paper substrates can be transported around rollers in the printer in the normal way.
The first crosslinker will depend on what crosslinkable polymeric substance is used in the process. Any material that may be placed in a liquid suitable for use in an ink jet may be used. Many materials are known to act as hardening or crosslinking agents for gelatin, see for example chapter 2 of xe2x80x9cThe Theory of the Photographic Processxe2x80x9d, Fourth Edition, edited by T. H. James and published by the Eastman Kodak Company, 1977. Crosslinkers for gelatin include metal salts, aldehydes, N-methylol compounds, diketone compounds, sulphonate esters and sulfonyl halides, S-triazines, and active olefins including bis-vinyl sulfonyl compounds.
Especially suitable materials as the first crosslinker for gelatin include aqueous solutions of aldehydes including formaldehyde, glyoxal and glutaraldehyde; and aqueous solutions of polyvalent metal salts such as Al3+, Cr3+, Fe3+, Ce4+. The preferred crosslinkers for the gelatins are glutaraldehyde and trivalent metal salts. Also preferred are the aqueous salts of Al(III) and Cr(III), including their chlorides, sulfates and nitrates. The preferred crosslinkers for the carboxylic acid polymers and copolymers are polyvalent metal salts. Most preferred are the aqueous salts of Al(III), Cr(III) and Zn(II), including their chlorides, sulfates and nitrates. The preferred crosslinkers for amine-bearing polymers are aldehydes and active vinyl compounds.
The material used in the ink jet cartridge may be any material that is compatible with the first crosslinker. The preferred carrier liquid for the first crosslinker is water, but other solvents or co-solvents may be present. For the preferred metal salts the solvent would be substantially water. Humectant agents that are commonly present in ink-jet inks may be present, and these include high boiling point liquids such as glycerol, ethylene glycol, diethylene glycol, triethylene glycol and 2-pyrrolidinone, as well as solids with a high affinity for water such as trimethylolpropane. Other substances present in the liquid in the ink jet cartridge may include anti-bacterial agents and thickening agents. The various substances present in the carrier liquid for the crosslinker must be compatible with the crosslinker and with the ink-jet mechanism.
Other fillers and additives such as known in the art may be used in the polymeric materials of the invention. Typical of such materials are bactericides, fillers, ultraviolet absorbers and brighteners.
The polymeric materials may be colored before or after ink jet printing. The colorants are those such as anionic dyes such as Tartrazine or Acid Blue 92, cationic dyes such as Rhodamine 6G or Crystal Violet, zwitterionic dyes such as Acid Fuchsin, or finely dispersed pigments such as titanium dioxide or copper phthalocyanine. If colorants are added in a wash after hardening they may be the same or different.
In a particularly preferred embodiment of the invention, a pattern of crosslinked polymer, for example, gelatin is formed on the first substrate, for example, a polyester sheet, and the uncrosslinked polymer is removed by washing with a solvent, for example, water. The second substrate, for example, a screen mesh, is contacted against the wetted crosslinked pattern, preferably in the presence of an adhesion promoting agent, and the assembly is allowed to dry. The pattern of crosslinked polymer attached to the second substrate is peeled away from the first substrate. The second substrate can then be contacted with a receiving material, ink is applied, and an inked image or pattern is applied to the receiving material.